Ring of Summoning Affinity (Inevitable)

This ring resembles a gear or cog. If the wearer can cast summon monster spells, the wearer adds arbiter to the 3rd-level list of monsters she can summon with those spells, adds zelekhut to the 7th-level list, adds kolyarut to the 8th-level list, and adds marut to the 9th-level list. Also, once per day on command the wearer can use this ring to summon an arbiter, as if by the summon monster III spell.